They report in Science journal that this corresponds to an additional 467 million hectares of forest that had never been reported or counted before. This is 4.67 million square kilometres, which is equivalent to an area bigger than all of India, and bigger than the 28 member states of the European Union.

The new figure was arrived at by taking a closer look at satellite data, and studying evidence from 213,795 half-hectare plots around the planet. Satellite monitors can easily identify rain forest, or the great conifer and birch forests of the north, but it is much harder to be sure of small plots of foliage in grassland.

Classed as forest

The scientists, led by researchers from the UN Food and Agriculture Organisation in Rome, are sure that some 1,327 million hectares of dryland had more than 10% tree cover in 2015, and 1,079 million hectares could be classed as forest.

The new estimate is important for two main reasons. One is that it provides statistical substance and reduces uncertainty for those climatologists who have to think about carbon sinks and sources in relation to what happens to atmospheric carbon in a rapidly warming world.

But the new data will also matter powerfully for conservation scientists concerned with the preservation of habitat for the wild things in a world in which, in one lifetime, the human population has grown threefold and is likely to hit the 9 billion mark in mid-century.

The world’s forests are essentially the sink for much of the carbon dioxide released by humans as they burn fossil fuels to drive global warming and climate change.

In addition, photosynthesis is the source not only of the world’s oxygen but the world’s food and fabric, and forests not only provide shelter and habitat for myriad other species but also help manage the flow of the world’s water.

It has therefore become important to know more, not just about forests, but about the planet’s tree population.

“Ground survey plot data indicates that a lot
of dryland vegetation assumed to be thicket,
shrubland, etc, is actually forest”

Another group surveyed 650,000 trees worldwide and came to a counter-intuitive conclusion that, when it came to the carbon budget, big old trees may matter more than young saplings − that is, the old stable forests were more important than plantations not just as habitat, but as helpmeets to humanity.

The new study extends knowledge of the world’s trees, but it also highlights a problem of definition, according to Paul Smith, secretary general of BGCI. The next problem is whether a satellite can actually see certain types of tree cover.

“The problem is that you have other native dryland vegetation types that can look pretty similar from the air to dry forest, such as thicket [a closed stand of bushes and climbers usually 3-7 metres tall] or shrubland [an open or closed stand of shrubs up to 2 metres tall].

“The bottom line is that you need to be on the ground to see these differences, hence the use of ground survey plot data in this study, which indicates that a lot of dryland vegetation assumed to be thicket, shrubland, etc, is actually forest.

“Of course, it isn’t just forests that sequester carbon – natural vegetation in all of its forms plays this critical role. Yet another reason to conserve it!”

The paradox is that not only does tree cover in Californian cities help reduce the costs of air conditioning, but it also adds value to properties, according to a separate study in the same journal.

In some parts of California, dryland forest counts as amenity. But in parts of Africa, Asia, Australia and South America, the separated stands of trees could hardly be more important: they offer shade, shelter and sustenance for the wild things, resources for humans, and they help prevent wind erosion and stabilise soil loss during sustained drought.

The new study, its authors say, offers an opportunity to think about new approaches to combat climate change, resist the advance of the deserts, and at the same time support the biodiversity and ecosystem services that, ultimately, underpin human survival. – Climate News Network

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